On the origin of line bisection error in hemianopia.

The contralesional line bisection error in hemianopia is a well-known clinical phenomenon. Its origin, however, is still unclear. We therefore investigated the causes of the hemianopic bisection error in 84 patients with unilateral homonymous hemianopia without visuospatial neglect. Our results suggest that the contralesional bisection error is neither a consequence of the visual field defect itself nor a manifestation of strategic adaptation of attention and eye movements into contralesional hemispace. Additional extrastriate brain injury, presumably to occipito-temporal areas including the occipital white matter, seems to be critical for the emergence of the contralesional bisection error that is frequently associated with but separable from homonymous hemianopia.